You've already have the drawings here on this forum which should give enough information to make or get made the transit chest from scratch. DS Solutions militaria in the UKicon sell repro hinges and catches.
https://www.milsurps.com/content.php...S.A.-No.15-Mk1
Reproduction, Metal Hardware Set for Chest No15 Mk1 (No4(T) Sniper Rifle)

I would have thought that you would want the Bren transit chest as is, as a militaria collectable, if it is in reasonable condition and the price is ok.